While Somdev steamrolled Thai wildcard Peerakiat Sirileuthaiwattana 6-2 6-1, Rastogi had to work hard for a 6-1 3-6 6-4 win over Australia's Brydan Klien at the Kallang tennis centre here.
Somdev will next take on 203rd-ranked Australian John Millman, who had to pull out all his experience to scrape past wildcard entrant and world number 284 Sergei Bubka 7-6(2) 6-7(5) 6-2 in a match lasting two hours and 29 minutes.
Rastogi will clash with former top-20 Russian Dmitry Tursonov, who outplayed sixth seed Ivo Minar of the Czech Republic 6-2,6-4.
"I started well, but lost my game midway in the match and also played a bad second set, It's great to come back from being broken two times in the third set."I'm also happy to have played with a cool head after having to wait on a couple of occasions with my opponent using time to recover from cramps at crucial moments," Rastogi said after the match